Hi Hazelelponi,
Thank you for your thoughtful responses.
Great questions. You are questioning the persons underlying motivations. That would be a likely culprit and probably the right answer in so many cases.
I tried to not make the question about myself in particular but you probably put my post and my screen name together and logically came to the conclusion that I was referring to myself. Admittedly I have my struggles and that did lead to my question.
Paraphrasing your words...
"When you are under sin you're a slave to your desires and passions..." and "The moment you have saving faith, that heart which was once sin becomes renewed in Christ"
So the thing that is missing is the saving faith. Imagine you are in the world. Maybe you don't have societal morality. Maybe you know you are broken and sinful. Maybe you desire to be freed from the bonds of slavery to sin. But no amount of prayer alters "your desires and passions". Therefore you must not have the indwelling Holy Spirit and therefore you must lack "Saving Faith". But why? How can a person who is "under sin" have saving faith?
There is a missing piece to the puzzle.
The missing piece may be God - or it could be a simple misunderstanding of what being saved or having a saving repentance looks like.
Here's the issue - saving faith doesn't mean your somehow perfect on day 1. It's simply a change in heart, after that, it's a lifetime of growing sanctification walking lockstep with God's Holy Spirit.
We are still in fleshly bodies so we will sin and err, we will then repent and go forward with life. We will have times of trial, and times of wondrous success.
Usually a good measuring stick is what is the change in a person...
Paul Washer (one of my favorite pastors) explained it like this.
Unsaved - A man is getting ready to head out the door, running late for a meeting at work, frustrated and with a million things on his mind. His wife stops him as he's hurriedly heading for the door and asks him to take out the trash.
Frustrated he yells at her "can't you see I'm late for the meeting?! No I won't take the trash out! You do it!" (Or something like that)
He goes to work and goes to the meeting feeling right about his actions.
3 months later the man comes to a saving faith in Christ.
There comes another day, again rushing out the door late for a meeting, and again his wife stops him and asks him to take out the trash on his way out the door.
Again he yells at her "Can't you see I'm late?! No I can't take the trash out you do it! I have to get to this meeting" and he slams the door on the way out.
All the way to work he feels bad for losing his temper and yelling at his wife, he just can't get it out of his head that he's done wrong.
He goes into work and is heading for the meeting, but he's still bothered about his behavior. He runs into his boss on the way to the meeting and says I'm going to be a few minutes late, there's something I have to do.
So he goes into his office and calls his wife and apologizes for yelling at her and asks for her forgiveness. After hanging up he says a quick prayer asking God to forgive him, then goes to the meeting...
Here what has changed isn't necessarily his actions, but his relation to his sin. Where once he felt right in his actions, they now bring him remorse and repentance.
Make sense?
So if you don't have a true saving faith, it's likely you'll simply not feel bad when you sin. You'll just run around just like before feeling right about yourself.
A good video is this: